Some systems define a slug as the part of a URL that identifies a page in human-readable keywords. It is usually the end part of the URL (specifically of the path / pathinfo part), which can be interpreted as the name of the resource, similar to the basename in a filename or the title of a page. The name is based on the use of the word slug in the news media to indicate a short name given to an article for internal use.

This is my best guess. I have never used it. NPM and JS are not fun for me. Like look at those dependencies.